This application outlines a projected study of the components of the fibrinolytic system. Specifically, it is proposed to: (1) Isolate and characterize proenzymes of urokinase from human plasma and a human epidermoid carcinoma (HEp 3) cells in culture; (2) Identify and purify specific inhibitors of urokinase from human placenta, HEp 3 cell culture, and platelets; and . (3) To develop improved methods for quantitation of the above fibrinolytic components. Because these proteins are present in trace amounts in most biological materials, an extremely selective and powerful approach -- immunoaffinity chromatography -- will be used. Anti-urokinase Ig Sepharose 4B will be use for the isolation of proenzymes of urokinase, while a specific anti-placenta inhibitor - Ig Sepharose 4B will be used to purifyinhibitors of urokinase. The proposed studies on the isolation and characterization of these proteins are expected to contribute to our understanding of the role of the proenzyme of urokinase in the fibrinolytic system of the plasma, to generate pure proenzymes of urokinase and inhibitors which are of potential therapeutic significance in thromboembolic and hemorrhagic diseases, and to provide methods of potential diagnostic utility in fibrinolytic disorders.